1. Field of the Invention
This invention relates to devices and methods for the direct application of chemical substances to selected plants at specific locations thereon.
2. Background Art
The conventional method of applying chemical substance to vegetation is by spraying, sprinkling or sowing solutions or mixtures of the chemicals on the whole plant area. Such "broadcast" methods reduce the desired concentrations on the specific plants to be treated, increase the cost of the chemicals, and subject vegetation far removed from the treatment area to the chemicals due to "drift," "vaporization," "translocation," or "leaching".
To avoid these difficulties associated with the broadcast methods, the individual application of chemicals has been made by hand to selected plants. Selective application has permitted the use of highly potent but relatively safe non-selective herbicides for the control of weeds and other undesirable vegetation. A preferred kind of non-selective herbicide is a 41% solution of isopropylamine salt of N-(phosphonomethyl) glicine, as further described in U.S. Pat. Nos. 3,799,758 and 4,405,531, and sold under the trademark "ROUNDUP" by the Monsanto Company, Agricultural Products Div., St. Louis, Missouri, 63167.
As disclosed in Laughlin U.S. Pat. No. 2,988,841, mechanical devices have been proposed for the direct application of chemical substances to selected plants at specific locations thereon An applicator such as a brush or pad is traversed across the area of vegetation at a pre-selected height, speed and angle, so as to produce a treatment zone without affecting underlying vegetation. Such a mechanical device includes height controlling wheels and a push handle or tractive support, or applicator brushes or pads are adjustably mounted on a rake-like structure.
Mechanical devices for the direct application of chemical substances to plants have been manufactured and sold as attachments to tractors Hardy et al. U.S. Pat. No. 4,187,638 discloses a rope wick applicator in the form of an elongated pipe having a number of exposed portions of wick protruding from the pipe at spaced locations. Similarly, an applicator has been manufactured and sold by Ex-Cell-O Corporation, Century Engineering Division, Cedar Rapids, Iowa 52401, in the form of an elongated pipe having its lower outer surface covered with a carpet fed with chemical solution.
Weed control at golf courses has been an especially difficult task. As described by Steve M. Batten in his article "Those Irrepressible, Incredible, Impossible Grassy Weeds!" USGA Green Section RECORD, September/October 1984 pp. 1-4, millions of dollars are spent annually and thousands of hours are devoted to golf course weed control. Weed control methods include scalping, deep-set vertical mowing, turning off irrigation, hand removal, excavation, and starvation by eliminating normal fertilization. Spot application of nonselective herbicide is typically made with hand-held sprayers, plastic squeeze bottles, hypodermic syringes, and paint brushes. Spot application requires the judgment of a person to determine what is a weed or where to place the herbicide. For this reason, this type of weed control is hard to automate or conduct with large tractors or maintenance vehicles. However, there are methods to selectively place herbicides such as "ROUNDUP" with large implements. Rope wick applicators can paint the top half of tall fescue or smutgrass above the grown height of desired turfgrasses. Weed kill results by translocation of the "ROUNDUP".
Rope wick or pad applicators have not been sufficiently accurate to selectively kill undesirable vegetation that extends only slightly above the desired vegetation, without causing some damage to the desired vegetation. This basic problem has been found to be related to a number of subsidiary problems including unstable operation of the applicator, undue complexity, inability to cover large areas in a reasonable time period, and the influence of uneven ground, clumps of weeds and foreign objects.